Cyclic phosphorus compounds structures

Interest has also continued in studies of the aromaticity of other unsaturated cyclic phosphorus compounds. A theoretical study of the 1,2-diphosphacyclooctatetraene system (228) has concluded that the ring system is perfectly planar when it has a global charge of —2 or +2, in contrast to the 1,2-diaza analogue which adopts a distorted, non-planar structure in the same oxidation states. However, it is thought unlikely that the phosphorus heterocycle will form planar metallocene complexes with metal ions. Theoretical and experimental studies have also been reported for the lone pair 671-aromatic anions P4 (229) and the arsenic analogue As4 . Both... 

Spontaneous alternating copolymerizations of two cyclic phosphorus compounds, 2-phenyl-l,3,2-dloxaphospholane 11 and 2-phenoxy-1,3,2-dloxaphospholane 20, with several electrophilic monomers were discussed. As the electrophilic monomers, /3-proplolactone 13, 3-hydroxypropanesulfonlc acid lactone (propane-sultone) 15, acrylic acid 16, acrylamide 17, acrylate were sucessfully copolymerized with 11. At temperatures lower than those of copolymerization, the combinations of 11—13, 11—16, 11—-17 and 11—acrylate produced trioxyphosphorane derivatives having spiro-ring structures, which were significant in two... 

A number of preparations of mixed halogenophosphoranes from tervalent phosphorus-fluorine compounds have been reported. For example, acyclic and cyclic fluorine compounds have been converted to phosphoranes, such as (36) and (37), by treatment with chlorine. Similar reactions leading to AA-dialkylaminodichlorodifluorophosphoranes (38) have been described and the stability of (38) to exchange processes commented upon. iVA-Dialkylaminotetraiodophosphoranes (39) have been prepared from AA-dialkylaminodichlorophosphines and lithium iodide, although no detailed physical evidence for the structure of these unusual compounds has yet been reported. The preparation of bis-(A-alkylamino)difluorophosphoranes (4) has been described above (see Section lA). 

The reagent does not replace nitrogen atoms, and N-alkyl or N-aryl anthranilic acids yield 2,l-benzisothiazoline-3-thiones (94) on heating with phosphorus pentasulfide in xylene. Curiously, when alkyl iV-arylanthranilates are treated in the same way, only a very small proportion—less than 10%— of 94 is obtained. The major product (80%) is the cyclic phosphorus-containing compound (95), the identification of which gives some clue about the structures of possible intermediates.122... 

The reason for this behavior in the case of the double-bonded structures ( A -type phosphorus) is the easy dimerization of the P=C bond. Tricoordinate planar (or nearly planar) phosphorus ( B - and C -type bonding) can be stabilized by repyramidalization when the cyclic electron delocalization is disturbed or lost (e.g., in a chemical reaction). The fine balance between these energetic effects cannot easily be predicted by using analogies or other simple models. Such predictions, however, can be made by using the sophisticated methods of computational chemistry, leaving the field of the chemistry of the aromatic phosphorus compounds an interesting research area with unexpected results in the future. 

During the past four years we have determined the crystal structure of over thirty cyclic containing phosphorus compounds and have established that their structures in the solid state and in solution in general are similar (1,2). Recent x-ray structures in the bis(biphenylylene) series (3,A) show steric effects as the size of R increases. 

A third type of five-membered cyclic oxyphosphorane is represented by derivatives of the 1,3,2-dioxaphospholene -10,12,18 and the 1,3,2-dioxaphospholane ring systems. These compounds are made from the reactions of trivalent phosphorus compounds and certain mono- and dicarbonyl functions, (73).J5 Some a-diearbonyl structures furnish... 

The question of whether the phosphonitrilic chlorides have cyclic or linear structures has been frequently discussed in the literature. The structural evidence will be considered in Section lY, where it will be seen that the cyclic formulation is established beyond doubt for the trimer and tetramer, and is highly probable for the higher soluble polymers it will meanwhile be assumed for all compounds of formula (PNX2) . For reasons considered in Section II, C the petrol-insoluble fraction (PNCUln PCls is believed to consist of a mixture of linear polymers. The two series are related, in that the linear compounds of low molecular weight are intermediates in the formation of the cyclics by the ammonolysis of phosphorus pentachloride. 

In conclusion, we may expect further advances in understanding factors controlling structural and conformational preferences of cyclic oxyphosphoranes, both from an experimental as well as a theoretical point of view. As the area continues to develop, the use of oxyphosphoranes as models in mechanistic interpretation should enhance our understanding of pathways followed in nucleophilic displacement reactions of tetracoordinated phosphorus compounds. Acknowledgment... 

There follows a series of four papers by Houalla et al. on further extensions of the Atherton-Todd reaction to the synthesis of pentacoordinated phosphorus compounds with the phosphorus as a heteratom within a wide variety of macrocyclic structures. The first paper22 describes the reaction of 1-hydridobicyclophosphoranes containing a secondary amine group (e.g. 56) with (57) which leads to a cyclic / /s(bicyclophosphorane)-(58), as well as the symmetrical bicyclophosphorane (59). The opportunity to exploit the reaction in the synthesis of novel macrocyclic structures was too good to miss and compounds such as (62) were prepared from the corresponding 6/s-phosphorane (60) and the Ws-phenol (61).23... 

In 1907 Tafel and Wassmuth treated pyrrolidone with phosphorus pentachloride and isolated a compound, m.p. 50-51°C, for which the cyclic imidoyl chloride structure XX has been postulated. 

Pavan Kumar et al. <2006NJC717> investigated the reaction of diethyl azodicarboxylate (DEAD) or diisopropyl azodicarboxylate (DIAD) with cyclic phosphates or phosphoramides in order to determine the structural preferences in spirocyclic penta- and hexacoordinate aminophosphoranes. They found that sulfur would coordinate to phosphorus to form the [3.3.0] bicyclic compounds 94-96. 

Coordination of [(t-C4H9)2P(=Se)I] with molecular iodine furnishes a 1 1 adduct that crystallises as cyclic dimer in the solid state (Figure 46).57 From each I2 molecule within the structure, one atom acts as acceptor towards selenium, and the other one becomes very weak donor towards the iodine atom bonded to phosphorus. This compound fulfills the requirements of a soft-soft base pair . As in the structure of the parent donor molecule [(t-C4Hg)2P(=Se)I],... 

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